macOS Time Machine 📅 2026-02-06

Fixing Mac Time Machine Backup Failure: Network Connection Errors

Encountering Time Machine backup failures due to network issues on macOS can be disruptive, preventing critical data protection. This guide provides immediate mitigation and best-practice solutions to diagnose and resolve common network connection errors, ensuring your Time Machine backups to a network-attached storage (NAS) or server are reliable.

🚨 Symptoms & Diagnosis¶

Identifying the precise error is the first step towards a resolution. Time Machine network failures often manifest with clear messages:

"Time Machine can’t access the backup disk"
"The network backup disk could not be accessed because there was a problem with the network username or password"
Error Codes:
- OSStatus error 57
- OSStatus error 89
- 0x80070057

Log snippets (found in /var/log/system.log or via log show):

backupd: Failed to mount backup disk
smbd: connection refused

Root Cause: These errors typically stem from SMB/AFP authentication failures, network share unmounting issues (especially after sleep or reboot), SMB3 protocol mismatches, or network impediments like firewalls. Sparsebundle corruption can also contribute.

🛠️ Solutions¶

Proceed through these solutions systematically. Start with immediate mitigation, then move to more permanent fixes if the issue persists.

Immediate Mitigation: Remount Network Share and Clear Credentials

This quick fix attempts to re-establish the network connection and ensures correct credentials are used for mounting the Time Machine share, often resolving transient network issues.

Open Connect to Server:
- From the Finder, click on Go in the menu bar, then select Connect to Server... (or press Command + K).
Enter Server Address:
- In the "Server Address" field, enter the full path to your Time Machine share. Replace IP_ADDRESS with your NAS IP address or hostname, and sharename with the actual share name (e.g., timemachine).
```
smb://192.168.1.100/timemachine
```
Connect with Credentials:
- Click Connect. When prompted, enter the username and password registered with your NAS or network share for Time Machine. Ensure "Remember this password in my keychain" is unchecked for troubleshooting if you suspect keychain corruption, or checked if you want it saved for convenience once verified.
Select Backup Disk in Time Machine:
- Open System Settings (or System Preferences on older macOS versions) > General > Time Machine.
- Click Select Disk....
- Choose the newly mounted network volume from the list.
Initiate Backup:
- From the Time Machine menu bar icon, select Back Up Now.

Best Practice Fix: Reset Time Machine, Verify SMB3, and Repair Sparsebundle¶

Best Practice Fix: Reset Time Machine Preferences, Add to Login Items, and Verify Backup Health

This comprehensive approach addresses potential deeper issues including corrupt Time Machine preferences, unreliable share mounting, and integrity problems with the backup bundle itself.

Data Loss Warning

The steps involving sudo rm -f and "erase and reselect disk" are destructive and will delete configuration files or existing backups. Ensure you understand the implications before proceeding. It is highly recommended to attempt other fixes first.

Unmount All Network Shares:
- Open Finder. Locate any mounted network volumes in the sidebar under "Locations" and click the Eject button next to each one.
Clear Corrupt Keychain Entries:
- Open Keychain Access (Applications > Utilities > Keychain Access).
- In the search bar, type timemachine or the IP/hostname of your NAS.
- Delete any entries related to your Time Machine network share credentials. This forces macOS to prompt for new credentials.
Reset Time Machine Preferences (Terminal):
- Open Terminal (Applications > Utilities > Terminal).
- Temporarily disable Time Machine and remove its preference file. This helps clear potentially corrupted settings.
```
sudo tmutil disable
sudo rm -f /Library/Preferences/com.apple.TimeMachine.plist
```
- Re-enable Time Machine, specifying the path to your network share's sparsebundle. Note: Replace /Volumes/Backup.sparsebundle with the actual path to your Time Machine sparsebundle once it's mounted. If it's not yet mounted, you might need to mount it manually first (as in the Quick Fix) or simply sudo tmutil enable and select it via System Settings.
```
sudo tmutil enable
```
- Then, go to System Settings > General > Time Machine and Add Backup Disk... again, selecting your NAS share and providing credentials.
Add Share as Login Item:
- Manually mount your Time Machine network share (as per the "Immediate Mitigation" steps).
- Go to System Settings > General > Login Items.
- Under "Open at Login", click the + button.
- Navigate to /Volumes/ in the sidebar, select your mounted network share, and click Add. You can optionally check "Hide" to keep it from opening a Finder window at login. This ensures the share is available when your Mac starts.
Verify Backup Integrity:
- Ensure your network share is mounted.
- Hold down the Option key and click the Time Machine icon in the menu bar.
- Select Verify Backups. This process can take a long time depending on your backup size.
- Alternatively, use the Terminal command:
```
tmutil verifychecksums /Volumes/Backup.sparsebundle
```
- Note: Replace /Volumes/Backup.sparsebundle with the actual path to your Time Machine sparsebundle.
Repair Sparsebundle (Disk Utility):
- If verification reports issues, locate your .sparsebundle file on the mounted network share. Double-click it to mount it as a disk image.
- Open Disk Utility (Applications > Utilities).
- In the sidebar, select the mounted Time Machine disk image (it will appear as a virtual disk).
- Click First Aid and follow the prompts to run a check and repair.
Erase and Reselect Disk (Last Resort):
- If all else fails and your existing backups are not critical or are severely corrupted, you may need to start fresh.
- In System Settings > General > Time Machine, select the problematic disk and click Remove Disk.
- Then, select Add Backup Disk... and choose the network share again. Time Machine will prompt to erase the disk and begin a new full backup.

🧩 Technical Context (Visualized)¶

Time Machine on macOS relies on the backupd daemon to manage backups. For network destinations, it mounts remote shares, typically using SMB (Server Message Block) or historically AFP (Apple Filing Protocol) over NetBIOS/SMB3 protocols. The actual backup data is stored within a .sparsebundle file on this network share. Failures often occur during the authentication, mounting, or data access phases due to network configuration, credential mismatches, or issues with the sparsebundle itself.

graph TD
    A[macOS Time Machine] -- "> B{"Initiate Backup (backupd)"};
    B" --> C{Attempt Network Share Mount};
    C -- SMB/AFP Protocol --> D[NAS/Server with Time Machine Share];
    D -- Authentication/Credentials --> E{Keychain Access};
    E -- Success --> F{Mount Network Share};
    E -- "Failure (Incorrect Credentials)" --> G(Error: "Network username or password problem");
    F -- "Network Obstruction (Firewall/NAT)" --> H(Error: "Can't access backup disk");
    F -- SMB3 Mismatch/Unmount --> H;
    F -- Access Sparsebundle --> I["Sparsebundle (.sparsebundle)"];
    I -- Corruption/Access Issue --> J(Error: OSStatus 57, 89);
    I -- Success --> K[Perform Data Backup];
    K --> L[Backup Complete];
    G --> M[Troubleshoot Credentials/Network];
    H --> M;
    J --> N[Repair/Recreate Sparsebundle];

✅ Verification¶

After applying any solutions, verify that Time Machine is functioning correctly:

Check Time Machine Status:
```
tmutil status | grep -i 'backup phase'
```
This command shows the current status of Time Machine, including any active backup phases.
List Recent Backups:
```
tmutil listbackups
```
Confirm that new backups appear in the list after a successful run.
Review Time Machine Logs for Errors:
```
log show --predicate 'subsystem == "com.apple.TimeMachine"' --last 1h | grep -i error
```
This command filters system logs for Time Machine-specific errors within the last hour. Adjust --last 1h as needed.

📦 Prerequisites¶

To effectively troubleshoot and resolve these issues, you will need:

macOS Ventura (or newer) or an equivalent macOS version.
Administrator privileges on your Mac.
Access to the Terminal application.
A NAS (Network-Attached Storage) or server with SMB3 enabled for optimal Time Machine compatibility.
Access to Disk Utility for sparsebundle repair.